1. Field of the Invention
This invention relates to a modular switch system for bidirectional programmable switching of DC to several gigahertz signals.
2. Background of Information
Numerous switches have been designed for diverse applications. Typically, they are designed to operate within a specified frequency band. For instance, for control applications relays or logic are typically designed to operate from DC to about 3,000 Hz. For audio/video applications relays or integrated circuits (ICs) operate from 10 Hz to 10 MHz. For baseband (BB) and local area networks (LANs) mechanical switches, relays or ICs designed to operate from about 100 Hz to 100 MHz are typically used. For cable TV (CATV) and broadcast applications, mechanical switches, relays or diodes/ICs are used to switch signals in the 10 MHz to 550 MHz band. For master antenna television (MATV) and broad band cable (XCABLE) applications, a patch panel, relays or diodes/ICs are used to switch signals from 5 MHz to 1000 MHz. In satellite television receive only (TVRO), and multichannel multipoint distribution system (MMDS) applications, patch panels, coaxial switches, relays or diodes/ICs are used to switch signals in the 270 to 1750 MHZ and 1900 to 2300 MHZ bands, respectively. Finally, patch panels, specially designed electromagnetic relays, coaxial switches, diodes or monolithic microwave integrated circuit (MMIC) and applications specific integrated circuit (ASIC) based circuit elements are used to switch 1 to 40 GHz microwave signals. The switching devices or combinations of switching devices used for any particular application depends to a large extent upon the frequency band of interest, power levels of the switched signals, and the speed of switching required.
Although switches designed for any specific application have evolved to a high degree of performance and reliability, they are generally not adaptable for diversified application due to the use of different connectors, interfaces and connection requirements by the diverse users of the various frequency bands. Generally, switches designed to pass DC (direct current) are not suitable for RF (radio frequency) switching applications, and RF switches typically block DC. Switches designed for microwave applications are typically hundreds of times more expensive than an A/B selector switch such as used for a TV video game. Furthermore, different segments of the industry have adopted control systems for switching which are not compatible with those of other segments.
As frequency increases, the insertion loss increases, the isolation decreases and the return loss (impedance mismatch) increases, creating unwanted multiple reflections, transmission errors and increasing transmission loss. For these and other reasons, switches which are optimized for control functions are typically not suitable for higher frequency than audio or telephony, and switches optimized for the microwave spectrum, for example, such as the C-band terrestrial microwave and satellite downlink bands of 3,700 to 4,200 MHz (typically 50 ohm and using type N, BNC or SMA coaxial or waveguide connectors), will not work over the multi-octave CATV band of 30 to 450 MHz (typically 75 ohm and using type F connectors).
With the increasing proliferation of communications products and services, and the merging of the hereto largely independent telephony, video and digital technologies into a unified market place delivering voice, facsimile and data communications, interactive on-demand video home entertainment and consumer services over what is being referred to as the information superhighway, a growing need is evolving for switching capability covering all of these diverse technologies. With some 500 channels of video being planned, combined telephony, data and video delivery over the same medium (twisted pair, coaxial cable, fiber optics or RF), the rapidly growing availability for peripherals able to generate, process, scramble, decode, store, retrieve, transmit and receive this information stream is creating a need for low-loss, high isolation, bidirectional, broadband, programmable switches capable of selectively connecting and routing multiple signal sources to multiple output devices by direct routing or by switching a myriad of processing equipment into the loop.